In the opera, the chorus singers play a prominent role. Each of the opera’s four acts or parts features a grand tableau. This was a hallmark of the operas Verdi wrote with the patriotic librettist Temistocle Solera. The best way to express unified fervour and belief, Verdi and Solera demonstrated, was with the chorus. So rather than its previous function in Italian operas, of setting scenes and providing local colour, Verdi puts the chorus at the forefront of his drama.

At the point in the score when 'Va pensiero' is sung, the Hebrews are being held captive in Babylon. The Babylonians have threatened to kill them, which sparks an argument between the High Priest of Baal, Abigaille and King Nabucco (Nebuchadnezzar). Abigaille is determined to destroy the tribe, including Nabucco’s own daughter Fenena, and tricks Nabucco into signing their death warrant. When he realizes what he has done, Nabucco begs Abigaille for mercy, but it is too late.

On the banks of the Euphrates, the slaves, ignorant of these events, are dreaming of the homeland they saw destroyed in the first act of the opera. The violence and the vehemence of Abigaille and Nabucco’s argument is still evident in the brooding orchestral introduction to this second scene, but the Hebrews are untouched by it, and remain prayerful. Moving away from the dark flat keys that have dominated the first scene, Verdi composed this chorus in a warm F sharp major.

The chorus sings as though with one voice; their gently sweeping melody and the basic harmonies give the impression of a folk song-like innocence and simplicity. Solera’s text – inspired by Psalm 137 – is more of a lament. The country the slaves are describing is now gone. It is the tension between the music and its message that gives the chorus its power.

After the first muted statement of the theme, the chorus surges towards the phrase ‘O, mia patria, sì bella e perduta!’ (Oh, my country, so beautiful and lost!). This inspires an outspoken fanfare of defiance, swinging between very soft and very loud. After a more pensive passage, the initial theme returns. Now, however, it is accompanied by a winding chromatic line, which places a question mark over the slaves’ hopes of ever returning home.

Verdi and Solera’s prayer has unmistakable potency. During the 19th century, the chorus – and Nabucco as a whole – became an inseparable part of the mythology surrounding the reunification of Italy, and ‘Va pensiero’ was sung by massed forces at Verdi’s funeral. Highlighting the parallels between the Hebrews’ lot and the nationalists’ hopes of reviving Italy, people drew allegorical strength from Verdi’s opera. Some modern scholars have sought to distinguish the facts from the myths, but no one denies the power of this stirring chorus.